Yes my home town has been all over the broadcast media today. It seems that MOD cop Chris Swallow (!) took some film of what he thinks could have been a panther on the railway at Winston Rd. railway bridge. To watch the film which lasts over one minute click here
On my first viewing I thought it looked like a dog but would a dog “tightrope walk” along a single rail? If it is a big cat then perhaps the built up nature of the area makes it an unlikely one for an escaped/released/imagined big cat to be wandering in.
If you look at the map you’ll see the bridge where Old Luss Road meets Winston Road. You can see Kildonan Drive which is mentioned in the BBC article. The family Bigrab lived in Lochranza Drive (see junction with Kildonan) until 2005 and the kids’ school is nearby.